This invention relates to the conversion of mechanical energy present in waves on the surface of bodies of water to useful energy, and particularly to improvements in recently developed apparatus performing such function.
In co-pending U.S. patent applications Ser. No. 09/379,421, filed Aug. 8, 1999 and Ser. No. 09/763,247, filed Feb. 20, 2001 both by Carroll and both assigned to the assignee hereof (the subject matter of both applications being incorporated by reference herein), wave energy converters (WECs) are disclosed comprising elongated, generally (but not necessarily) hollow tube-like members disposed in vertical and preferably completely submerged orientation beneath the surface of a body of water (e.g., an ocean) preferably experiencing large surface waves on a fairly regular basis.
During operation, pressure variations between the top and bottom ends of the vertically elongated, submerged member caused by over-passing surface waves cause relative movements of a piston (e.g., the member itself or a piston disposed within a hollow space within the member) for driving an energy converting transducer.
Experience with such WECs has demonstrated that they can be the basis of a new generation of non-polluting and cost efficient energy sources. A problem with the use of such WECS, particularly in large bodies of water, is that the surface waves are highly variable both in amplitude and shape. Desired goals in the use of such WECs are that efficient operation be obtainable over a wide range of surface wave conditions and that the WECs can survive even the worst storm conditions. These goals are met in accordance with the present invention.
In a preferred embodiment of the invention, an elongated, neutrally or slightly buoyant first member is disposed in generally upright orientation at a selected depth beneath the mean water level of a body of water. The first member is hollow, with a closed top end and an open bottom end. The first member is mounted, for vertical movements along a path, on a second member comprising a float disposed within the hollow member. The member is also secured to a mechanical energy transducer, e.g., a hydraulic cylinder, for converting vertical movements of the member, in response to over-passing surface waves, to useful energy.
A principal feature of the inventive WECs is that they can accommodate a large range of different size surface waves producing large amplitudes of motion of the movable member while not damaging the apparatus or requiring an exceptionally large mechanical energy transducer. To this end: a) extra large vertical motions of the movable member are accommodated by end-of-stroke buffering with shock-absorbing elements; b) the entire system is gravity anchored to the water body floor, thus allowing lifting of the entire apparatus off the water bed in response to excessive upward movements of the moveable member; c) the moveable member is connected to the mechanical energy transducer by a stroke reducing linkage, e.g., a crank or lever, allowing a long travel of the moveable member but a far shorter travel of the moveable portion of the energy transducer, e.g., a piston of an hydraulic cylinder; d) pressure relief valves (e.g., spring loaded doors) are provided for reducing excessively large pressure differentials caused by excessively large overpassing waves; and e) the vertically extending member is mounted on a base support by a universal joint allowing tilting of the member in response to circulating water movements. (In one embodiment, the vertically extending member is connected to one or more transducers for converting the tilting movements of the vertically extending member to useful energy.)
Intrinsic protection against adverse surface conditions is provided by the normal submerged position of the apparatus. Additional protection is provided by selectively ballasting the apparatus for further sinking the apparatus towards or to the water floor. The selective ballasting mechanism is additionally useful for changing the buoyancy of the movable member in response to changing conditions, e.g., changes in system buoyancy caused by marine growth on the apparatus.
For further isolation from possibly damaging surface conditions, various control and transducer mechanisms, and the like, are disposed within water tight boxes disposed beneath the bottom of the moveable member and preferably on a base member providing the aforementioned gravity anchor on the water floor.